The invention is directed to improvements in fuel injection apparatus for diesel engines. A fuel injection apparatus of this type is already known (U.S. Pat. No. 3,465,737), in which the injection pump is embodied as a pump/nozzle and the fuel injection quantity is determined by means of a hydraulically driven control slide inserted in an overflow channel. This control slide determines the effective supply stroke and develops the fuel injection quantity of the injection pump by means of blocking the return flow out of the pump work chamber; and the injection is terminated when this control slide opens the overflow channel and the injection pressure can be relieved. In this known apparatus each control slide is actuated by the control pressure of a separate injection pump, acting as a control pump, which is driven simultaneously with the pump/nozzle. The control line acts as a filling line also, so that negative influences retroactively exerted on the fuel injection and control must be expected. A further disadvantage is that the fuel injection only takes place, in the inner-dead-center position of the pump piston, when the piston connects the control line with the pump work chamber through an annular groove. This limits its applicability in high speed engines. The object of the invention is to prevent the mutual influencing of supply and control pressure and to enhance the fuel injection and quantity metering so that the fuel injection apparatus will also be used in high-speed diesel engines.